What is a kidney stone?
A kidney stone is a solid piece of material that forms in a kidney when substances that are normally found in the urine become highly concentrated. A stone may stay in the kidney or travel down the urinary tract. Kidney stones vary in size. A small stone may pass on its own, causing little or no pain. A larger stone may get stuck along the urinary tract and can block the flow of urine, causing severe pain or bleeding.
Kidney stones are one of the most common disorders of the urinary tract. Each year in the United States, people make more than a million visits to health care providers and more than 300,000 people go to emergency rooms for kidney stone problems.
Urolithiasis is the medical term used to describe stones occurring in the urinary tract. Other frequently used terms are urinary tract stone disease and nephrolithiasis. Terms that describe the location of the stone in the urinary tract are sometimes used. For example, a ureteral stone—or ureterolithiasis—is a kidney stone found in the ureter.
What is the urinary tract?
The urinary tract is the body’s drainage system for removing wastes and extra water. The urinary tract includes two kidneys, two ureters, a bladder, and a urethra. The kidneys are two bean-shaped organs, each about the size of a fist. They are located near the middle of the back, just below the rib cage, one on each side of the spine.
Every day, the two kidneys process about 200 quarts of blood to produce about 1 to 2 quarts of urine, composed of wastes and extra water. The urine flows from the kidneys to the bladder through tubes called ureters. The bladder stores urine until releasing it through urination. When the bladder empties, urine flows out of the body through a tube called the urethra at the bottom of the bladder.
No exact information about the incidence of kidney stones in children is available, but many kidney specialists report seeing more children with this condition in recent years. While kidney stones are more common in adults, they do occur in infants, children, and teenagers from all races and ethnicities
What causes kidney stones in children?
Kidney stones can form when substances in the urine—such as calcium, magnesium, oxalate, and phosphorous—become highly concentrated due to one or more causes:
Defects in the urinary tract may block the flow of urine and create pools of urine. In stagnant urine, stone-forming substances tend to settle together into stones. Up to one-third of children who have stones have an anatomic abnormality in their urinary tract.
Kidney stones may have a genetic cause. In other words, the tendency to form stones can run in families due to inherited factors.
An unhealthy lifestyle may make children more likely to have kidney stones. For example, drinking too little water or drinking the wrong types of fluids, such as soft drinks or drinks with caffeine, may cause substances in the urine to become too concentrated. Similarly, too much sodium, or salt, in the diet may contribute to more chemicals in the urine, causing an increase in stone formation. Some doctors believe increases in obesity rates, less active lifestyles, and diets higher in salt may be causing more children to have kidney stones.
Sometimes, a urinary tract infection can cause kidney stones to form. Some types of bacteria in the urinary tract break down urea—a waste product removed from the blood by the kidneys—into substances that form stones.
Some children have metabolic disorders that lead to kidney stones. Metabolism is the way the body uses digested food for energy, including the process of breaking down food, using food’s nutrients in the body, and removing the wastes that remain. The most common metabolic disorder that causes kidney stones in children is hypercalciuria, which causes extra calcium to collect in the urine. Other more rare metabolic conditions involve problems breaking down oxalate, a substance made in the body and found in some foods. These conditions include hyperoxaluria, too much oxalate in the urine, and oxalosis, characterized by deposits of oxalate and calcium in the body’s tissues. Another rare metabolic condition called cystinuria can cause kidney stones. Cystinuria is an excess of the amino acid cystine in the urine. Amino acids are the building blocks of proteins.
What are the signs and symptoms of kidney stones in children?
Children with kidney stones may experience:
Pain while urinating
See blood in urine
Feel a sharp pain in the back or lower abdomen (short/ long term)
Experience nausea and vomiting with pain
Some children who have small stones that pass easily through the urinary tract may not have any symptoms.
What types of kidney stones occur in children?
Four major types of kidney stones can form:
Calcium stones are the most common type of kidney stone and occur in two major forms: calcium oxalate and calcium phosphate. Calcium oxalate stones are more common. Calcium oxalate stone formation may be caused by high calcium and high oxalate excretion. Calcium phosphate stones are caused by the combination of high urine calcium and alkaline urine, meaning the urine has a high pH.
Uric acid stones form when the urine is persistently acidic. A diet rich in purines—substances found in animal protein such as meats, fish, and shellfish—may increase uric acid in urine. If uric acid becomes concentrated in the urine, it can settle and form a stone by itself or along with calcium.
Struvite stones result from kidney infections. Eliminating infected stones from the urinary tract and staying infection-free can prevent more struvite stones.
Cystine stones result from a genetic disorder that causes cystine to leak through the kidneys and into the urine, forming crystals that tend to accumulate into stones.
Kidney stones vary in size and shape. Stones may be as small as a grain of sand or as large as a pearl.
Some stones are even as big as golf balls. Stones may be smooth or jagged and are usually yellow or brown.
What do kidney stones look like?
Treatment for kidney stones usually depends on their size and what they are made of, as well as whether they are causing pain or obstructing the urinary tract. Kidney stones may be treated by a general practitioner or by a urologist—a doctor who specializes in the urinary tract. Small stones usually pass through the urinary tract without treatment. Still, the person may need pain medication and should drink lots of fluids to help move the stone along. Pain control may consist of oral or intravenous (IV) medication, depending on the duration and severity of the pain. IV fluids may be needed if the person becomes dehydrated from vomiting or an inability to drink. A person with a larger stone, or one that blocks urine flow and causes great pain, may need more urgent treatment, such as
Shock wave lithotripsy (SWL): A machine called a lithotripter is used to crush the kidney stone. The procedure is performed by a urologist on an outpatient basis and anesthesia is used. In shock wave lithotripsy, the person lies on a table or, less commonly, in a tub of water above the lithotripter. The lithotripter generates shock waves that pass through the person’s body to break the kidney stone into smaller pieces to pass more readily through the urinary tract.
Ureteroscopy: A ureteroscope—a long, tubelike instrument with an eyepiece—is used to find and retrieve the stone with a small basket or to break the stone up with laser energy. The procedure is performed by a urologist in a hospital with anesthesia. The urologist inserts the ureteroscope into the person’s urethra and slides the scope through the bladder and into the ureter.The urologist removes the stone or, if the stone is large, uses a flexible fiber attached to a laser generator to break the stone into smaller pieces that can pass out of the body in the urine. The person usually goes home the same day.
How are kidney stones in children diagnosed?
To diagnose kidney stones, the health care provider will perform a physical exam and take a medical history. The medical history may include questions about family history of kidney stones, diet, GI problems, and other diseases and disorders. The health care provider may perform urine, blood, and imaging tests, such as an x ray or computerized tomography (CT) scan to complete the diagnosis.
Urinalysis: Urinalysis is testing of a urine sample. The urine sample is collected in a special container in a health care provider’s office or commercial facility and can be tested in the same location or sent to a lab for analysis. Urinalysis can show whether the person has an infection or the urine contains substances that form stones.
Blood test: A blood test involves drawing blood at a health care provider’s office or commercial facility and sending the sample to a lab for analysis. The blood test can show biochemical problems that can lead to kidney stones.
Abdominal x ray, or KUB (kidney ureter bladder) x ray: An abdominal x ray is a picture created using radiation and recorded on film or on a computer. The amount of radiation used is small. An x ray is performed at a hospital or outpatient center by an x-ray technician, and the images are interpreted by a radiologist—a doctor who specializes in medical imaging. Anesthesia is not needed. The person will lie on a table or stand during the x ray. The x-ray machine is positioned over the abdominal area. The person will hold his or her breath as the picture is taken so that the picture will not be blurry. The person may be asked to change position for additional pictures. The x rays can show the location of stones in the kidney or urinary tract.
Tips: You may consider taking a laxative the day before the KUB x ray so that stools will not obscure the pictures of the kidneys.
Ultrasound: Ultrasound uses a device, called a transducer, that bounces safe, painless sound waves off organs to create an image of their structure. An abdominal ultrasound can create images of the entire urinary tract. The procedure is performed in a health care provider’s office, outpatient center, or hospital by a specially trained technician, and the images are interpreted by a radiologist—a doctor who specializes in medical imaging; anesthesia is not needed. The images can show the location of any stones. This test does not expose children to radiation, unlike some other imaging tests. Although other tests are more useful in detecting very small stones or stones in the lower portion of the ureter, ultrasound is considered by many health care providers to be the best screening test to look for stones.
CT scans: CT scans use a combination of x rays and computer technology to create three-dimensional (3-D) images. A CT scan may include the injection of a special dye, called contrast medium. CT scans require the person to lie on a table that slides into a tunnel-shaped device where the x rays are taken. The procedure is performed in an outpatient center or hospital by an x-ray technician, and the images are interpreted by a radiologist. Anesthesia is not needed. CT scans can show stone locations and conditions that may have caused the stone to form.
How are kidney stones in children treated?
Percutaneous nephrolithotomy: In this procedure, a wire-thin viewing instrument called nephroscope is used to locate and remove the stone. The procedure is performed by a urologist in a hospital with anesthesia. During the procedure, a tube is inserted directly into the kidney through a small incision in the person’s back. For large stones, an ultrasonic probe that acts as a lithotripter may be needed to deliver shock waves that break the stone into small pieces that can be removed more easily. The person may have to stay in the hospital for several days after the procedure and may have a small tube called a nephrostomy tube inserted through the skin into the kidney. The nephrostomy tube drains urine and any residual stone fragments from the kidney into a urine collection bag. The tube is usually left in the kidney for 2 or 3 days while the person remains in the hospital.
How are kidney stones in children prevented?
To prevent kidney stones, health care providers and their patients must understand what is causing the stones to form. Especially in children with suspected metabolic abnormalities or with recurrent stones, a 24-hour urine collection is obtained to measure daily urine volume and to determine if any underlying mineral abnormality is making a child more likely to form stones. Based on the analysis of the collected urine, the treatment can be individualized to address a metabolic problem.
The health care provider may ask the person to collect urine for 24 hours after a stone has passed or been removed to measure daily urine volume and mineral levels. Producing too little urine or having a mineral abnormality can make a person more likely to form stones. Kidney stones may be prevented through changes in eating, diet, and nutrition and medications.
In all circumstances, children should drink plenty of fluids to keep the urine diluted and flush away substances that could form kidney stones. Urine should be almost clear.
Points to Remember
A kidney stone is a solid piece of material that forms in a kidney when substances that are normally found in the urine become highly concentrated.
Kidney stones are one of the most common disorders of the urinary tract.
Kidney stones occur in infants, children, and teenagers from all races and ethnicities.
Kidney stones in children are diagnosed using a combination of urine, blood, and imaging tests.
The treatment for a kidney stone usually depends on its size and composition as well as whether it is causing symptoms of pain or obstructing the urinary tract.
Small stones usually pass through the urinary tract without treatment. Still, children will often require pain control and encouragement to drink lots of fluids to help move the stone along.
Children with larger stones, or stones that block urine flow and cause great pain, may need to be hospitalized for more urgent treatment.
Hospital treatments may include shock wave lithotripsy (SWL), removal of the stone with a ureteroscope, lithotripsy with a ureteroscope, or percutaneous nephrolithotomy.
To prevent recurrent kidney stones, health care providers and their patients must understand what is causing the stones to form.
In all circumstances, children should drink plenty of fluids to keep the urine diluted and flush away substances that could form kidney stones. Urine should be almost clear.
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